OLED Pixel Driving Circuit With Coupling Capacitor Gray-Scale Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Reducing the cross-voltage between VDD and VSS in OLED displays to conserve power results in a decreased data voltage range, preventing the display of certain gray scales due to negative data voltage requirements that exceed the capabilities of the drive chip.
Innovation Solution
A pixel driving circuit incorporating a writing transistor, storage capacitor, coupling capacitor, and drive transistor, along with additional control transistors, to adjust the voltage at the first node during the light emitting stage using a coupling capacitor, ensuring the drive current meets the required brightness levels without exceeding the data voltage range provided by the drive chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the cross-voltage between VDD and VSS is reduced to lower power consumption, then energy consumption is reduced, but the data voltage range decreases causing inability to display certain gray scales
Solution Approach 1:
The patent segments the voltage control function into two independent parts: the data signal terminal provides a base data voltage, and the coupling capacitor terminal provides an adjustable compensation voltage. This segmentation allows the drive transistor to receive a combined voltage that achieves the required drive current without requiring the data signal to cover the full voltage range, thus enabling low cross-voltage operation while maintaining complete gray scale display capability.
Solution Approach 2:
The patent changes the voltage parameter at the gate of the drive transistor by introducing a coupling capacitor that can adjust its voltage independently. This allows the gate voltage to be optimized for the reduced cross-voltage condition, enabling the drive transistor to generate sufficient drive current even when the overall cross-voltage between VDD and VSS is reduced for lower power consumption.
2Use of energy by moving object
If the cross-voltage between VDD and VSS is reduced, then power consumption is reduced, but negative data voltages are required which the drive chip cannot provide
Solution Approach 1:
The coupling capacitor acts as an intermediary element between the control voltage terminal and the gate of the drive transistor. It receives an adjustable voltage from the control terminal and combines it with the data voltage from the data signal terminal, producing the required gate voltage without requiring the data signal itself to go negative. This intermediary function allows the drive chip to operate within its positive voltage capability range.
3Illumination intensity
If the voltage at the first node is adjusted during light emitting stage, then the drive current can meet brightness requirements, but additional circuit components are required
Solution Approach 1:
The coupling capacitor is designed to serve multiple functions: it compensates for threshold voltage variations of the drive transistor, adjusts the gate voltage to meet brightness requirements, and enables the circuit to operate with reduced cross-voltage. By integrating these multiple functions into a single component, the patent achieves the required brightness control without proportionally increasing circuit complexity.
Data Source
AI summary
A pixel driving circuit and a driving method therefor, and a display panel and a display apparatus. The pixel driving circuit comprises a write-in transistor, a driving transistor, a storage capacitor, a coupling capacitor and a light-emitting unit, wherein one electrode of the storage capacitor and a gate electrode of the driving transistor are both electrically connected to a first node; and one electrode of the coupling capacitor is electrically connected to a control voltage end, and the other electrode thereof is electrically connected to the first node, and the coupling capacitor is configured to adjust the voltage of the first node in a light emission phase, such that the voltage of the first node is converted from a first voltage into a second voltage.